1. Field of the Invention
This invention relates to a device for correcting positional deviation and variation in reduced scale produced when an object having contour lines, for example, moire stripes created thereon is photographed on film, and for representing the contour lines on the film in the form of either exact contour drawing or polar coordinates.
2. Description of the Prior Art
There is a method of creating contour lines or moire stripes on the surface of a body to thereby examine the configuration of the body by measuring the coordinates or by depicting contour lines. Means for creating moire stripes on an object is well-known and need not particularly be described herein. When contour lines or moire stripes have been created, the distance between adjacent lines or stripes in the direction of depth (the direction of photography) may be regarded as known. For example, in FIG. 3 of the accompanying drawings, if BD and NC are considered to be moire stripes, .DELTA.H1 is known. When these are photographed by the use of a camera having a focal length f, there will occur inconveniences as will hereinafter be described.
First, as is clearly shown in FIG. 4, contour line NC is photographed on film 5 with a positional deviation with respect to contour line BD, and vertex A is also deviated.
Further, it is seen from FIG. 3 that the reduced scale of contour line BD on the film is f/H, that of contour line NC is f/(H - .DELTA.H1), and that of the region near the vertex A is f/(H - .DELTA.H2). Thus, when the exposed film is used to carry out an analysis, it will be necessary to correct the positional deviation and reduced scale for the information on the film 5. However, as regards, for example, N'C' which is an orthogonal projection of contour line NC on a reference plane 12 (the plane on which contour line BD exists), points n and c' at which the point N' and C' are imaged on the film 5 are on the same reduced scale and in proper positional relationship with points b and d at which the points B and D on the reference plane 12 are imaged on the film. If it is assumed that the film surface 5 and the reference plane 12 are parallel and that N' On is the optical axis, the point n is called the principal point (which is in accord with the vertical point). It is also clear from the drawing that points N and N' are imaged at point n in overlapping relationship. Designated by 0 is the center of the photographic objective.
On the film 5, the relation between P and P' will now be considered on the assumption that nc=P and nc'=P'. ##EQU1## Also, since NC=N'C', ##EQU2## where .DELTA.H1 is known as previously mentioned, P is known (measurable) distance from the point photographed on the film to the principal point n, and H can be known as the photographic reference plane (even if it is unknown, it can easily be known by making some contrivances in the stage of photography). Thus, a proper amount of correction may be obtained from equation (1).